A prolific Scottish painter, illustrator, and commercial artist, McLaren grew up in Cardenden, Fife, before going to college in Edinburgh. He graduated from Edinburgh College of Art in 1944. For many years, he was a regular illustrator for The Radio Times, The Listener, and other magazines; he also painted commissions for public buildings, often in trompe l'oeil, including murals at Wemyss Castle, Hopetoun House, and Hawthornden Castle. In 2009, a film "William McLaren: an atist out of time" was made, and shown at the 2010 Glasgow Film Festival "Great Scots" series.